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Stratigraphy, paleomagnetism, and cosmogenic-isotope burial ages of fossil-bearing strata within Riverbluff Cave, Greene County, Missouri

Published online by Cambridge University Press:  24 April 2017

Charles W. Rovey II*
Affiliation:
Department of Geography, Geology, and Planning, Missouri State University, 901 S. National, Springfield, Missouri 65897, USA
Greg Balco
Affiliation:
Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, California 94709, USA
Matt Forir
Affiliation:
Missouri Institute of Natural Science, 2327 W. Farm Road 190, Springfield, Missouri 65810, USA
William F. Kean
Affiliation:
Department of Geosciences, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, USA
*
*Corresponding author at: Department of Geography, Geology, and Planning, Missouri State University, 901 S. National, Springfield, Missouri 65897, USA. E-mail address: charlesrovey@missouristate.edu (C.W. Rovey).

Abstract

Riverbluff Cave, in Greene County, Missouri, is a short single passage between the James River and its direct tributary, Ward Branch. Before stream incision the cave functioned as a spillway/piracy between the two streams during high-discharge events and accumulated a sequence of stratified fluvial sediments within the cave. Five cosmogenic-nuclide burial ages for these sediments range from 0.984 to 0.570 Ma. These ages are consistent with both the stratigraphic order of the samples and the inferred position of the Matuyama/Brunhes paleomagnetic boundary. These ages indicate that sandy channel-facies deposits derived from Ward Branch entrances began to accumulate within the cave as early as 0.984±0.065 Ma. This facies is capped by highly fossiliferous gravel beds dated at 0.658±0.065 Ma, which contain abundant mammoth bones (possibly Mammuthus trogontherii) and other vertebrates. The high concentration implies that this deposit may record some type of mass-mortality event. By 0.570±0.072 Ma, all Ward Branch entrances had been abandoned because of incision, and a laminated red clay derived from backflow from flooding along the James River capped the older channel sediments.

Information

Type
Research Article
Copyright
Copyright © University of Washington. Published by Cambridge University Press, 2017 

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